1. Field of the Invention
The present invention relates to a combustion appliance with flame blocking device, which can be installed in a garage, a basement, a storehouse or other places where flammable materials generating flammable gases, such as gasoline, thinner or benzine, are kept.
2. Description of the Related Art
Conventionally, water heaters with flame blocking devices are provided with a hot-water storage chamber R1 and a combustion chamber R2, which are arranged one above the other inside a hollow cylindrical main body 11, as shown in FIG. 4. In a known water heater, the combustion chamber R2 is provided with an air supply port 13a through which air is taken in, a main burner 22 combusting fuel gas, and a pilot burner 4 for carrying the flame over the main burner 22. An exhaust pipe 16, which passes through the axis of the hot-water storage chamber R1 and opens to the top of the main body 11, exhausts fuel gas in the combustion chamber R2 to the outside of the water heater. Furthermore, a flame arrester 27 (flame blocking device) is provided at the air supply port 13a. 
Other aspects of the remaining configuration are as explained for the embodiments of the present invention, so that a further explanation of the corresponding numerals has been omitted.
In this water heater with flame blocking device, water that has been fed into the hot-water storage chamber R1 is heated by heat exchange with hot combustion exhaust gas that passes through the exhaust pipe 16 after combustion in the main burner 22 provided in the combustion chamber R2. The heated water is stored as hot water of a certain temperature, which can be furnished to the outside as appropriate.
If this water heater is installed near flammable material generating flammable gases, there is the risk that the flammable gases intrude through the air supply port 13a of the hot-water heater, and the flame of the combustion chamber R2 is propagated and makes the flammable material catch fire. Therefore, a flame arrester 27 is provided to prevent a leakage of the flame in the combustion chamber R2 through the air supply port 13a to the outside.
The flame arrester 27 is a plate-shaped member made of metal and provided uniformly with a multitude of tiny apertures, such as punched metal or expand metal. Each flammable gas has a so-called quenching distance, and flames are not propagated along a path when the gap is below this quenching distance. In order to utilize this quenching distance, the size of the apertures in the flame arrester 27 is set no greater than a diameter of about 1.6 mm.
However, due to their small size, the apertures of the flame arrester 27 are easily clogged by fine particles, such as fluff and dust. Therefore, when clogged, there is the risk that the air supplied to the combustion chamber R2 becomes insufficient, leading to an incomplete combustion, which may cause carbon monoxide poisoning.
In order to overcome this problem, it is an object of the present invention to provide a combustion appliance with flame blocking device, in which incomplete combustion due to blocking of the air supply path can be prevented.
A combustion appliance with flame blocking device according to claim 1 of the present invention solving the above-described problems includes:
a main burner, which burns a mixture of fuel gas and air for combustion;
an air supply path, which supplies air for combustion to a combustion chamber in which the main burner is provided;
a flame blocking device, which obstructs the passage of flames by partitioning the air supply path into a plurality of apertures;
a pilot burner disposed inside the combustion chamber, which burns a mixture of fuel gas and air for combustion that is sucked from a pilot air supply port;
a flame detecting element, which outputs a detection signal corresponding to the combustion state of the pilot burner; and
an incomplete combustion prevention device, which prevents incomplete combustion with the main burner in response to the signal from the flame detecting element;
wherein, when a flow of combustion exhaust generated by combustion with the main burner stagnates, the pilot burner sucks in combustion exhaust from the pilot air supply port.
In accordance with a combustion appliance with flame blocking device according to claim 2, in the combustion appliance with flame blocking device according to claim 1,
the flame detecting element is a primary thermocouple;
a secondary thermocouple which detects the stagnancy of the combustion exhaust by an increase in temperature is provided; and
the secondary thermocouple is connected in series but with opposite polarity to the primary thermocouple.
In the above-described combustion appliance with flame blocking device according to claim 1 of the present invention, when fine particles such as fluff or dust enters the air supply path and clogs the flame blocking device, the supply and exhaust of air to/from the combustion chamber cannot be performed smoothly and the combustion exhaust tends to stagnate.
In this situation, the pilot burner sucks in this combustion exhaust with low oxygen concentration as the air for combustion from the pilot air supply port, so that the combustion state of the pilot burner deteriorates before the main burner performs incomplete combustion, and the flame of the pilot burner is lifted due to the lack of oxygen. The flame detection element detects this change in the combustion state, and the incomplete combustion prevention device is activated.
In the combustion appliance with flame blocking device according to claim 2 of the present invention, the secondary thermocouple is connected with a polarity that is opposite to that of the primary thermocouple, so that its electromotive force acts negatively and reduces the combined electromotive force with the primary thermocouple.
When the apertures of the blocking device clog up, the flame of the pilot burner is lifted due to the lack of oxygen and the electromotive force of the primary thermocouple is decreased. Moreover, since the detected temperature of the secondary thermocouple increases, the combined electromotive force drops sharply below that of the normal combustion state, so that the lack of oxygen can be detected with high sensitivity, and the incomplete combustion prevention device is activated.